Public defender Michael Corriere said it was a "tactical" decision to prevent prosecutors from presenting further damaging letters that Ballard wrote from prison after the four murders he committed last summer.

The death-penalty trial will resume Tuesday, when District Attorney John Morganelli said he will have brief rebuttal testimony before closing arguments begin. Then the jury will be charged and deliberate Ballard's fate.

The jury is deciding whether Ballard should be executed or sentenced to life in prison without parole.

Monday marked the third day of testimony in the defense's case. Among developments: It was revealed that in the days leading up to murder, Ballard and his girlfriend exchanged text messages in which they expressed love and talked about marriage and having a baby.

In total, 86 text messages were sent between Ballard and Denise Merhi in the five days before Ballard murdered her along with her father, her grandfather and a neighbor in Northampton. The messages offered further details into the moments leading up to killings that prosecutors say were punishment for Merhi seeing other men.

In the messages, Ballard calls Merhi "Mrs. Ballard," suggests they have a baby together, and sends her the phone number of a district judge, who can perform marriage ceremonies. In responses, Merhi says she is getting off birth control, "can't wait" to have a baby inside her, and calls herself "his wife."

But the messages also reveal tensions lurking underneath: Ballard says that "99 percent" of the time Merhi "rocks," but asks her to work on the "1 percent" because it makes him jealous.

She expresses reservations about telling her family she's having a baby and, the day before the murders, twice says they "need to talk" about whether they'll wed.

State police trooper Raymond Judge, the case's lead investigator, was called by the defense to detail the text messages.

In them, Merhi refers to Ballard as "Superman" and Ballard tells her she makes him feel "like Superman." On the day he committed the four murders, he was wearing a Superman T-shirt.

Also Monday, a defense medical expert testified that damage to Ballard's brain has left it like a runaway car, lacking the needed breaks to control his impulses and override thoughts of aggression.

Ballard — who has admitted the murders— has damage to his brain's frontal lobe, which mediates judgment, and his amygdale, which processes emotional reactions, said University of Pennsylvania neuropsychologist Ruben Gur.

"It's like a car that starts racing when your foot is already on the breaks," Gur, who examined medical scans of Ballard's brain, told the Northampton County jury.

"Overdrive, all the time?" asked Corriere.

"You could say that. That's a good analogy," Gur said.

Brain damage is a key factor that Ballard's attorneys are arguing in their bid to keep him off death. Gur is the second medical expert to testify to it, and his findings, while highly technical, are a critical piece of the defense's case.

As a result, Morganelli sought to cast doubt on Gur's qualifications and motivations, highlighting that Gur has testified as a defense witness in many capital cases at trial and on appeal, including in December for Allentown serial killer Harvey Robinson.

In that and other cases, Morganelli said, Gur used similar broken car analogies in arguing the effects of brain damage.

"You're part of a small group of experts who travel around the country and show up to say the defendant has brain damage, isn't that true?" Morganelli asked.

That prompted an objection from James Connell, another Ballard lawyer, who said Gur wouldn't be called as a witness if brain damage wasn't found. Morganelli withdrew his query without Gur's response.

Gur's findings are based on an analysis he did of an MRI and another brain scan that Ballard received. Damage to the frontal lobe is associated with mania, risk taking and antisocial behavior, Gur said. The amygdale governs threat response, he said.

In animal testing, doctors manipulating a monkey's amygdale can make it "just attack everything in sight," Gur said.

Last month, Ballard pleaded guilty to stabbing to death former girlfriend, Merhi, 39; her father, Dennis Marsh, 62; her grandfather, Alvin Marsh Jr., 87; and Steven Zernhelt, 53, a neighbor who heard screams at their 1917 Lincoln Ave. home and tried to help.

At the time of the June 26 killings, Ballard had recently been paroled on a 15- to 30-year sentence for stabbing and slitting the throat of an Allentown man in 1991, then stealing the dead man's wallet and car.

Gur is the second medical expert to conclude Ballard is brain damaged. On Friday, psychologist Gerald Cooke said fights, motor cycle accidents and other head injuries Ballard suffered as a youth have left him more susceptible to stress and alcohol and less able to control his emotions.

Corriere and Connell are seeking a life sentence for Ballard, arguing the brain damage, their client's rough childhood and overbearing jealousy helped cause him to "snap."

Morganelli says a death sentence is appropriate for a 37-year-old man who sought not only to murder his girlfriend, but to "punish her" for seeing other men by also slaying her family.

Prosecution testimony last week included graphic photos of the crime scene and the autopsies of the four victims. County Coroner Zachary Lysek recounted the blood-soaked home Ballard left in his wake and pathologist Samuel Land detailed the wounds each of the victims suffered.

One day was dominated by the statements of victims' family members, who spoke of nightmares of their loved ones being knifed to death, and of empty milestones like birthdays, graduations and weddings.